The invention relates generally to the field of earth anchors. In particular, the invention relates to earth anchors having load bearing elements in the form of a helix to serve as a foundation or anchor for buildings and other structures.
The use of earth anchors to provide a foundation or anchor for buildings or other structures is well known. A typical earth anchor for embedment within the ground has a central hub with one or more load bearing elements in the form of a spiral blade which extends radially outward from the central hub. Such earth anchors are turned into the ground to a desired depth, typically between about five to about forty feet, using a torque head that is typically mounted to a back hoe or front-end loader. The earth anchors may be used singly as foundations for structures such as billboards, traffic signs, light poles, utility poles, and the like. They may also be used in groups to found residential and light commercial buildings. Further, such earth anchors may be used as an anchoring device for guy wires, and to tie back retaining walls.
The load bearing elements of many prior art earth anchors are typically spacedly arranged in a manner that results in each element penetrating the soil at a different position, i.e., a subsequent element does not necessarily follow the path cut by a foregoing element. In addition, many prior art earth anchors have load bearing elements that are crudely shaped and only approximate a helix. Such an inexact arrangement and shape of the elements typically results in a high installation torque prohibiting the use of earth anchors in areas with very hard bedrock. The inexact arrangement and shape of the elements typically results from their manner of construction. The central hub is typically a square bar stock with machined ends. Helical blades are cut from plate steel, such as high strength carbon steel, and bent to approximate a helix. The blades are then welded to the hub.
Another feature of many earth anchors is that they have load bearing elements that are generally circular as viewed from either end of the hub. Such a shape maximizes the outer perimeter of the load bearing elements while minimizing the amount of penetration upon rotational installation. However, such a shape necessarily requires a large amount of material to construct. As such, the cost of such blades can be significant.
Many earth anchors are constructed of carbon steel that is hot dipped zinc galvanized. Carbon steel is often employed to construct the earth anchors because of its relatively low cost. However, carbon steel and zinc generally corrode at equal rates when embedded in the earth. To compensate for such corrosion, earth anchors are often constructed of an excessive amount of carbon steel to prevent corrosive failure. As such, the cost of the earth anchors is significantly increased. The installation torque is also higher because of the thicker members.
Water from surface runoff, irrigation and other sources typically can travel through relatively more permeable backfill placed along building grade beams and foundation walls to an interior or exterior foundation drain. Installation of earth anchors has been speculated to cause a water path that is cut down through the soil by the blades. Some of the water passing by the top of the earth anchor may be conducted down this path, possibly increasing the rate and depth of wetting. In expansive soils, some have speculated that this may result in greater heave. Hence, it would be desirable to provide improved earth anchors and methods for their use which require substantially less torque to introduce the earth anchors into the ground. It would be further desirable if such earth anchors were constructed in a way so as to reduce their overall cost while still providing an adequate load bearing or anchoring capacity. It would be further desirable to construct the earth anchors of a material that has better corrosion resistance and requires less material to construct, thereby further reducing installation torque and cost. It would be still further desirable to provide techniques for sealing water paths adjacent the earth anchor to reduce the chances of soil heave created by soil wetting.